Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations declare a non-read-only, non-idempotent, non-destructive append; the description reinforces this with 'Each call adds a new entry' and adds traits annotations cannot express — that the history is kept with the user's data export, that no tool reads it back, and that it does not replace facts stored via update_coach_profile or upsert_goal. That is real behavioral context beyond the structured fields.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loads the core action and constraints, then adds the important caveat about read-back. The middle enumeration of milestone types is somewhat list-like, but each sentence carries distinct information and none is filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists, so return values need no elaboration; the description still notes 'Returns the stored event.' Combined with the append-only semantics, sibling disambiguation and exclusion list, an agent has everything needed to call this correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% and the enum plus payload examples are already documented in the schema; the description's 'for example type=checkin' and payload gist largely restate that. Baseline 3 is appropriate since the schema carries the parameter burden.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

Opens with a specific verb+resource ('Append a dated milestone to the user's coaching history') and then enumerates the milestone kinds the type enum covers, so an agent knows exactly what this tool records. It explicitly differentiates itself from log_session and upsert_goal, which are the most confusable siblings.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives explicit when-to-use cases (check-in held, goal reviewed/achieved, deload advised, red flag raised, intake started/finished, profile changed) and explicit when-not-to-use cases ('Not for ordinary chat, logged workouts (log_session) or goal edits themselves (upsert_goal)'), naming the alternative tools by name.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.